Combination hf treating catalytic cracking process



June 30, 1953 A. P. LIEN ETAL COMBINATION HF TREATING CATALYTIC CRACKINGPROCESS Filed June 14, 1950 Patented June 30, 1953 COD/IBINATLON HFTREATING CATALYTIC CRACKING PROCESS Arthur P. Lien, Hammond, Ind., andBernardL. Evcring, Chicago, Ill., assignors to Standard Oil Company,Chicago, Ill., a corporation of Indiana Application June 14, 1950,Serial No. 168,112

6 Claims. (Cl. 196-14.11)

This invention relates to a process of producing high quality motor fuelfrom heavier-thangasoline hydrocarbons by a new and improved combinationof HF treating and catalytic cracking and it pertains more particularlyto processes wherein the catalytic cracking is eiected by silica aluminatype catalysts. -This is a continuation-in-part of our copendingapplication Ser.'No. 718,038, now U. S. 2,525,812, and also Ser. No.760,062, now U. S. 2,525,811.

An object of theinvention is to provide a method and means for obtainingmaximum yields of high quality motor fuel from catalytic crackingcharging stocks containing large amounts of sulfur compounds,objectionable polycyclic hydrocarbons, and/or other components which arenot eiliciently handled by catalytic cracking processes and/or which`may be detrimental in catalytic cracking systems.` A further object isto improve the effectiveness and eiiiciency of catalytic crackingsystems employing silica alumina type catalysts, i. e. to obtainincreased motor fuel production, decreased coke formation and superiorproduct quality. A still further object is to provide a process whereinthe catalyst used in the second step is promoted in situ by traces oftreating agent employed in the rst step so that the expense of removingsuch traces of treating agent is largely avoided so that the combinationof steps produces results heretofore unobtainable in the art. Otherobjects will be apparent as the detailed description of the inventionproceeds.

Brieflyl the invention contemplates the production of high quality motorfuel from heavierthan-gasoline charging stocks which have heretoforepresented serious problems to the rening industry. For example, a WestTexas gas oil may contain2 to 3% of sulfur and when such gas oil ischarged to a conventional catalytic cracking process the finishedgasoline will contain about .3% sulfur and the catalytic gas oil about11/2 to 2% of sulfur. By giving gas oil a preliminary treatment with HFand then subjecting it to substantially the same conditions of catalyticcracking, we obtain a marked and substantial increase in gasolineproduction per pass and a marked improvement in gasoline quality, thegasoline containing only about one-tenth as much sulfur and beingcharacterized by a higher A. P. I. gravity, a lower bromine number, anda greatly increased responsiveness to lead tetraethyl. In spite oftreating losses in the initial step the overall yield of gasoline may beas high as the yield that would be obtained from untreated chargingstock. The effective catalytic cracking capacity 'is markedly increased.The treating step itself eliminates sulfur and other undesirablecomponents and it may produce a utilizable Icy-product tar from materialwhich would otherwise be deposited as coke on the catalyst in the'ycracking step. Furthermore, the treating step may remove organicand/or'inorganic material from the charge that would otherwisecontaminate o-r deactivate'the catalyst and lead to lower conversion,undesirable product distribution, excessive gas Vand coke formation,etc.

The initial step of the process is a light treatment with HF, i. e. atreatment under such `mild conditions as to lavoid any substantialamount of cracking but which is sufficient to veliminate the bulk of thesulfur and other undesirable components in the gas oil. A lowtemperature treatment is described and claimed in U. S. 2,525,812. Inthe present invention, the initial treatmentis mild by virtue of thecorrelation of the time of contact, temperature and amount of HF whichis preferably in the range of about 5 to 50% by weight, although amountsmay be as high as 200 to 300% by weight. The temperature should be aboveF. and may be as high as 400 F. or more so that at least some of thesulfur can be removed as HzS.

The high temperature treating step results in` intermolecular chemicalcondensation of certain of the aromatic hydrocarbons to produceHiT-soluble polynuclear aromatic hydrocarbons which are extracted fromsaturated hydrocarbons, the HF serving both as a catalyst in thechemical reaction and as a solvent for effecting the extraction. Manygas oils and other hydrocarbon charging stocks which are higher boilingthan gasoline contain substantial Aamounts of polycyclic aromatics whichare insoluble in hydrogen fluoride but which are condensable in thepresence of hydrogen fluoride into higher molecular weight hydrogenfluoride-soluble hydrocarbons with liberation of hydrogen `(note U. S.2,525,810 and 2,525,809). f

rIhe treated charging stock, which may be of the distillate fuel or gasoil boiling range and which preferably contains not more than about 5%of hydrocarbons of the gasoline boiling range, may be separated fromgases or low boiling components as well as from the bulk of HF (extractphase) in a settling zone wherein the undesirable polycyclichydrocarbons and sulfur compounds associated therewith are withdrawn inthe bottom HF layer and the gases, including liberated hydrogen and HzS,are taken overhead. The dissolved HF in the treated charge may beremoved by a simple stripping oper-ation and the charge, which containsonly traces of HF, is then directly introduced into a catalytic crackingreactor containing a solid catalyst of the silica alumina type andoperated under conditions for converting the charge to motor fuel. Bythe expression silica alumina type We mean to include the so-called claytype or natural catalyst such as acid treated montmorillonite clay,synthetic or gel type silica alumina catalysts, silica magnesiacatalysts, silica alumina magnesia catalysts, catalysts prepared fromblast furnace slag, etc., either in the presence or absence ofadditional catalyst components and/or activators. In other words, thecracking catalysts may be of the type referred to by Webb and Ehrhardtin Properties of Cracking Catalysts, Petroleum Processing, January 1947.

Traces of HF remaining from the initial treat- -ment of our chargingstock may effect an in situ activation of the cracking catalyst so thatthe yield per pass of gasoline is substantially increased. At any rate,the net result of our combined process is the production of remarkablyhigh quality gasoline of low sulfur content, an increase in the capacityof the cracking unit, the substantial elimination of Ithe expense ofdefluorinating and a net increase in production of valuable Icy-productmaterials, the increase in .gasoline production made possible by thetreating step substantially -balancing losses due to by-product removalin the treating step.

The invention will 'be more clearly understood from the followingdescription read in conjunction with the accompanying drawing which isfaschematic flow diagram illustrating a practical application of ourinvention.

While the invention is `applicable to any heavier-than-gasolinehydrocarbon charging stock, up to and including reduced crudes, whichcontains components such as large amounts of sulfur, condensablearomatics, etc., which are deleterious'to or are ineiectively handled ina catalytic cracking system, rit will be described in connection withthe treatment of a heavy, high sulfur gas oil. Such high sulfur gas oilcharging stock is introduced through line I by pump II to line I2 Whereit meets HF from storage tank I3, line I4 and pump I5. Knot hole mixersor other mixing means may be employed for attaining intimate contact ofthe tWo streams in line I2 -and/or said intimate contact maybe obtained-in treating chamber I6 by mechanical stirrer II driven by motor I8.Instead of a stirred reactor, We may employ a packed or unpacked towerwith mixing oriiices, a circulating system of the type commonly employedfor effecting sulfuric acid alkylation or any other effective contactingmeans. Instead of the illustrated concurrent Vflow through the reactor,Ithe HF may be introzduced at the top thereof while the charge is in-Atroduced at the base, such countercurrent treatment being particularlydesirable in towers Where the treating is to be effected in acountercurrent manner andthe separation is effected in the tower itself,the treated material being in that case taken overhead while the HF andimpurities are Withdrawn from the base `of the tower. In the systemillustrated in the drawing, a mixture of HF and treated charging stockis withdrawn from vessel I6 by line I9 to settler 20, a cooler 2l beingemployed if the treating is at very high temperature.

The treating should be effected under relatively mild conditions so thatsulfur and/or other undesirable components may be removed from thecharging stock without materially changing its boiling range, i. e.without effecting substantial amounts of cracking. By effecting thetreatment at a temperature in the range of 150 to 400 F. or more, atleast a part of the sulfur compounds are converted into HzS in thetreating step. The preferred temperature of treatment is in the range of200 to 375 F. with best results being obtained at temperatures of `about250 to 330 F. The treating is effected under a pressure suiiicient tomaintain liquid phase conversion conditions, i. e. within a range ofabout 250 to 1000 p. s. i., or preferably about 500 to 800 p. s. i. Atthe highest treating temperatures the time of contact should besuiiciently short, substantially less than 10 minutes, and/or the amountof HF should be suiciently low, e. g. 5

to 50 volume per cent HF, so that no substantial cracking of thecharging s-tock takes place. At temperatures of the order of 200 to 330F., the time of contact in the reactor should be relatively long,usually within the range of about 20 to 200 minutes (the lowertemperatures requiring longer contact times). An hours contact time at330 F. is adequate, The treating conditions should in any case be suchas to effect condensation of -condensable `aromatics with removal ofsulfur so that hydrogen fluoride-insoluble material will be chiefly aparanic gas oil, substantially free from condensable aromatics andsulfur and containing only a small amount, preferably less than 5%, ofgasoline boiling range hydrocarbons including benzene and methylbenzenes.

If settler 20 is operated at cooling water .temperature, the treatedhydrocarbons which separate as an upper layer may be withdrawn directlythrough line 22 to gas oil stripper 23. Settler 20 may, however, operateat a higher -temperature in the range of about to 250 F. and Yin suchcases the Atreated gas oil may be Withdrawn through cooler 24 and coldsettler 25 for throwing out addition-al amounts of HF which may then berecycled directly by line 2E, thereby diminishing the load on thestripper Atower 23.

The I-IF layer from settler 20 is withdrawn from line 2l :and a part ofit may be recycled to treater IE via line I2. At the beginning of thetreating operation all of the hydrogen uoride soluble tarry materialwithdrawn from `the settlers 20 and 25 may thus be recycled to thereactor for the dual purpose of improving the catalyst effectiveness inthe reactor and for degrading the tar dissolved therein and obtainingmaximum yields of hydrogen fluoride-insoluble hydrocarbons, such as gasoil therefrom. When equilibrium conditions are established, there may befor example abo-ut 40% by weight of HF-soluble tar in reactor I6 Abasedon hydrogen fluoride therein.

The net production of tar (condensed aromatics, sulfur compounds, etc.which are soluble in HF) is withdrawn in HF solution through line 21a totar stripper 28 which is provided at its base with conventional heateror reboiler 29. The tar and sulfur adducts with HF are decomposed byheating to Z50-500 F. The overhead from this stripper is passed throughcondenser 30 to settler 3I in which the HF separates out as a lowerliquid land is Withdrawn through line 32 to storage tank I3. The upperlayer in settler 3I consists chiey of light hydrocarbons and it may berecycled through line 33 by pump 34 to serve as a stripping oil in tower28 by virtue of azeotrope formation with HF, any deilciency or excess oflight hydrocarbons .being supplied to or -removed from this circulatingsystem through line 35.

Tar and sulfur compounds are withdrawn. from the base of the stripperthrough line 28a and such tar may be utilized per se as a by-product oritv may be subjected to coking or cracking to form additional amounts ofgasoline.'

The HzS produced in the HF treating step is removed along with othergases from the top of settler through line 36 to knock back tower 31which is provided with cooling, scrubbing or reflux means 38 so thatmethane, H2S, HCl (from desalting) and other xed gases may be ventedthrough line 39 while HF and oondensible hydrocarbons are returned byline 40 to stripper 23.

Stripper 23 is provided with a suitable heater or reboiler 4l at itsbase and overhead from this stripper passes through condenser 42 tosettler 43. Liquid HF accumulates in the bottom of this settler and iswithdrawn through line 44 to storage tank I3. A light hydrocarbon iswithdrawn from the upper part of the settler through line 45 strippinggas in tower 23, any excess or deficiency of such light hydrocarbonsbeing removed from or supplied to the system through line 41.

The stripped gas oil leaving the base of stripper 23 through line 48 maypass through a preheater 49, then pick up hot regenerated catalyst fromthe base of standpipe and carry this catalyst into reactor 5l. Spentcatalyst from reactor 5I passes downwardly through standpipe 52, ispicked up by air introduced in line 53 and conveyed thereby in line 54to regenerator 55, regeneration gases being vented through line 55a. Thefluid type catalytic cracking system thus briefly and diagrammaticallyrepresented is now well known to those skilled in the art and requiresno detailed description. The catalyst-to-oil ratios employed may be inthe range of 2:1 to 20:1 on a weight basis, the cracking temperature maybe in the range of about -800 to 1000 F., e. g. about 900 F. and theweight space velocity may be in the range of about 0.2 to 20 pounds ofoil charged per hour per pound of catalyst in the reactor. In otherwords, the cracking conditions may be approximately the same as thoseheretofore employed for conventional gas oil stocks although somewhatsmaller amounts of catalyst cr higher throughputs may be obtained byvirtue of the promoting effect of the residual amounts of HF which areintroduced into the cracking system with the treated gas oil. While thefluid type catalytic cracking system has been illustrated in the drawingit should be understood that the invention is equally applicable tofixed bed systems and to moving bed systems. The catalyst itself is ofthe silica alumina type and may be either conventional Super Filtrol ora synthetic silica alumina catalyst of any type known to the art.

Apparently Super Filtrol and other silica alumina type crackingcatalysts generally are markedly improved in their activity by treatmentwith HF, which perhaps results in the formation of aluminum uosilicate.ln our process this activation of the catalyst is particularly eiectivebecause it is produced in situ. The traces of HF remaining in thetreated gas oil are thus eiectively removed therefrom in the crackingoperation and at the same time the eiectiveness of the catalyst isincreased so that higher conversions per pass are obtained with smalleramounts and recycled by pump 46 to serve as a t of carbon deposition onthe catalyst. Usually the amount of HF introduced is so small that'themake-up catalyst requirements in the cracking step are suicient to takecare of it.k It some cases, however, it may be necessary or desirable topass a portion of the treated gas oil through bauxite chambers or otherHF removal means 56 (note U. S. Patent 2,391,149). Our inventionminimizes the required HF removal and may entirely eliminate it.

The products from catalytic cracking reactor 5l' pass by line 5l totower 58 which may be provided with a settling section 59 at its base sothat catalyst slurry may be returned through line 60 to the streamentering the reactor and decanted oil may `be withdrawn through line 6|and either removed from the system or recycled through lines 62 and l2to the HF treating step. Heavy gas oil may be withdrawn as a side streamthrough line 63, recycled by lines 64 and I2 to the HF treating step,and/or recycled by lines 64 and Ella to the catalytic cracking step.Cycle gas oil from this process is usually in m-ost respects superior tothe untreated original gas oil charge `put if all of it is recycledthrough line 64a, a buildup in sulfur compounds or aromatics mightresult; at least a part of the gas oil stream should usually thereforeeither be withdrawn through line 63 or recycled through line l 2 to thetreating step in order to prevent any buildup of sulfur compounds oraromatics` in the catalytic cracking step. A light gas oil stream may bewithdrawn through line 65 and it likewise may be recycled either to theHF treating step or to the catalytic cracking step. Gasoline and lightercomponents are taken overhead through line 56 and condenser Sl' tosettler 68 from which any water from diluent steam in the cracking stepor otherwise accumulated in the system may be withdrawn through 69. Anygasoline produced in the HF treating or tar cracking and taken overheadfrom strippers 23 or 28 may be passed via lines 35 or 47 through line"lll, HF removal chambers 'H and line 'I2 to separator S8. Gases fromthis separator are compressed by compressor 13, liquid hydrocarbons arepumped by pump 14, and the combined stream is passed through line 15 tosuperatmospheric pressure fractionation system diagrammaticallyillustrated by tower 'I6 from which heavy naphtha is withdrawn throughline '11, and one or more lighter naphtha streams through lines 1B andlg. A C4 or l3x-C4 stream may be withdrawn. through line 8G and suchbutane or propane-butane mixtures may be introduced by line 8l and line70 to supply any deciency of stripping gas for towers 23 and 28respectively. Dry gas is removed from the system through line 82. Inactual practice of course a conventional absorber and stripper systemmay be employed instead of a simple tower but since this fractionationstep per se forms no part of the claimed invention it will not bedescribed in further detail.

From the above description it will be seen that we have accomplished theobjects of our invention. The mild treating step removes sulfurcompounds and/or polycyclic aromatics which are not readily amenable tocracking and makes possible the recovery of tar and sulfur compounds asutilizable lay-products. This particular method of pretreating thecatalytic cracking charging stock (coupled perhaps with traces of HF'left in the treated charging stock) results in greatly increasedcracking yields, substantially less carbon formation on the catalyst andan improved cracked gasoline which is less olenic, more amenable toimprovement by lead tetraethyl and which contains only about one-tenthas much sulfur as would be obtained by the cracking of the same stockWithout the initial treating step. The catalytic cracking apparentlyconcentrates the sulfur com-pounds in the cycle gas oil so that Whenthis gas oil is recycled to the HF treating step still further amountsof sulfur can be eliminated from the system and kept out of the iinalgasoline products. In fact, gas oils produced by catalytic or thermalcracking (such as continuous pressure still gas oil, coke still gas oil,vis breaker gas oil, etc.) are particularly suitable as originalcharging stocks to our process because such gas oils usually containlarge amounts of aromatics which are originally insoluble in HF butwhich are condensible to form ITF-soluble polycyclic aromatics withliberation of hydrogen. Our process thus eliminates from such catalyticcracking charging stocks the components which are most detrimental anddeleterious (polycyclic aromatics and sulfur cornpounds) with minimumtreating losses and maximum ultimate production of high qualitygasoline. The butane or propane-butane hydrocarbons produced in thecatalytic cracking step serve as stripping gases and form HF azeotropeswhich facilitate HF removal from the treated gas oil and the tarrespectively. Thus this new and improved unitary combinationaccomplishes results which have heretofore been unattainable in thecracking of low grade charging stocks yand particularly those containinglarge amounts of sulfur.

While We have described in detail a specic example of our invention,many alternative modifications, procedures and operating conditions willbe apparent from the above description to those skilled in the art. Whensalt bearing reduced crudes are employed the process will offer theadditional advantage of salt removal. While hydrogen is liberated in thearomatic condensation reaction, it is not necessarily present in the offgases, since it may be consumed by reacting With sulfur compounds or bysaturating oleiins. No specific details as to structural materials andgeneral safety precautions have been recited herein since those skilledin the art are familiar With the handling of HF in view of itscommercial utilization in effecting alkylation.

We claim:

1, The method of obtaining valuable products from a hydrocarbon chargingstock which is higher boiling than gasoline and which containssubstantial amounts of polyoyclic aromatics which are insoluble inhydrogen fluoride but which are condensable in the presence of hydrogenfluoride into higher molecular weight hydrogen fluoride-solublehydrocarbons with liberation of hydrogen, which method comprisestreating said charging stock with a catalyst consisting essentially ofhydrogen uoride in a iirst conversion zone at a temperature above 150 F.but not substantially 'above 400 F. under conditions for eiectingintermolecular chemical condensation of said polycyclic aromatichydrocarbons into hydrogen iiuoride-soluble condensed aromatics ofhigher molecular weight with simultaneous liberation of hydrogen,separating the condensed polycyclic aromatics and the hydrogen nuoridein which they are dissolved from hydrogen iiuoride-insolublehydrocarbons consisting essentially of a gas oil having a substantiallyreduced content of condensable aromatics, subsequently contacting saidgas oil with a solid siliceous cracking catalyst under catalyticcracking conditions for converting said gas oil into hydrocarbons of thegasoline boiling range.

2. The method of .obtaining valuable products from a hydrocarboncharging stock which is higher boiling than gasoline and which containssubstantial amounts of polycyclic aromatics which are insoluble inhydrogen fluoride but which are condensable in the presence of hydrogeniluoride into higher molecular weight hydrocarbons with liberation ofhydrogen, which method comprises treating said charging stock with acatalyst consisting essentially of hydrogen iiuoride in a iirstconversion zone at a temperature above 200 F. but not substantiallyabove375 F. under conditions for effecting intermolecular chemicalcondensation of said polycyclic aromatic hydrocarbons into hydrogenfluoride with the soluble condensed aromatic compounds of highermolecular Weight with simultaneous liberation of hydrogen, separatingthe condensed aromatic compounds, together with hydrogen uoride in whichthey are dissolved, from hydrogen iiuoride-insoluble hydrocarbonsconsisting essentially of a gas oil which is relatively free fromcondensable. aromatics, subsequently contacting said gas oil with asolid siliceous catalytic cracking catalyst under conditions foreffecting as the predominant reaction a conversion of said gas oil intohydrocarbons of the gasoline boiling range and separating said lastnamed hydrocarbons from higher boiling and lower boiling components.

3. The method of claim 2 wherein the rst conversion Zone is maintainedunder a 4pressure in the range of 250 to 1000 pounds per square inch andfor a time of contact in the range of about 10 to 200 minutes With anamount of hydrogen iluoride in the range of about 10 to 200 volume percent based on stock charged.

4. The method of claim 2 wherein the charging stock also containssubstantial amounts of sulfur compounds, which method includes thefurther step of' converting at least a part of the sulfur compounds toHzS in the treating step and separating HzS from liquid products.

5; The method of claim 2 which includes the step of recycling at least apart of said higher boiling components to the treating step.

6. The method of claim 2 wherein the original charging stock is ahydrocarbon fraction of the gas oil boiling range produced as aby-product in a cracking operation.

' ARTHUR P. LIEN.

BERNARD L. EVERING.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 2,279,550 Benedict et al Apr. 14, 1942 2,291,885 Egloi Aug. 4,1942 2,375,675 Matuszak May 8, 1945 2,377,613 Conn June 5, 19452,378,762 Frey June 19, 1945 2,525,812 Lien et al Oct. 17, 1950

1. THE METHOD OF OBTAINING VALUABLE PRODUCTS FROM A HYDROCARBON CHARGINGSTOCK WHICH IS HIGHER BOILING THAN GASOLINE AND WHICH CONTAINSSUBSTANTIAL AMOUNTS OF POLYCYCLIC AROMATICS WHICH ARE INSOLUBLE INHYDROGEN FLUORIDE BUT WHICH ARE CONDENSABLE IN THE PRESENCE OF HYDROGENFLUORIDE INTO HIGHER MOLECULAR WEIGHT HYDROGEN FLUORIDE-SOLUBLEHYDROCARBONS WITH LIBERATION OF HYDROGEN, WHICH METHOD COMPRISESTREATING SAID CHARGING STOCK WITH A CATALYST CONSISTING ESSENTIALLY OFHYDROGEN FLUORIDE IN A FIRST CONVERSION ZONE AT A TEMPERATURE ABOVE 150*F. BUT NOT SUBSTANTIALLY ABOVE 40* F. UNDER CONDITIONS FOR EFFECTINGINTERMOLECULAR CHEMICAL CONDENSATION OF SAID POLYCYCLIC AROMATICHYDROCARBONS INTO HYDROGEN FLUORIDE-SOLUBLE CONDENSED AROMATICS OFHIGHER MOLECULAR WEIGHT WITH SIMULTANEOUS LIBERATION OF HYDROGEN,SEPARATING THE CONDENSED POLYCYCLIC AROMATICS AND THE HYDROGEN FLUORIDEIN WHICH THEY ARE DISSOLVED FROM HYDRO-